Variety of xenobiotics, including therapeutically used vitamin D analogues or environmental and alimentary endocrine disruptors, may interfere with vitamin D receptor (VDR) signalling, with serious physiological or pathophysiological consequences. Therefore, it is of topical interest to have reliable and efficient in vitro screening tool for identification of agonists and activators of human VDR. We present here two novel stably transfected human reporter cell lines allowing rapid, high-throughput and selective identification of VDR agonists and activators. Human colon adenocarcinoma cells LS180 were stably transfected with reporter plasmids CYP24_minP-pNL2.1[Nluc/Hygro] (IZ-CYP24 cells: contain -326/-46 sequence from human CYP24A1 promoter) or VDREI3_SV40-pNL2.1[Nluc/Hygro] (IZ-VDRE cells: contain three copies of vitamin D response elements VDRE-I from human CYP24A1 promoter). Both cell lines remained fully functional for over two months in the culture and also after cryopreservation. Luciferase inductions ranged from 10-fold to 25-fold (RLU 106-107) and from 30-fold to 80-fold (RLU 103-104) in IZ-VDRE and IZ-CYP24 cells, respectively. Time-course analyses revealed that detection of VDR activators is possible as soon as after 8 hours of incubation. Cell lines were highly selective towards VDR agonists, displaying no cross-activation by retinoids, thyroids and steroids. As a proof of concept, we used IZ-VDRE and IZ-CYP24 cells for profiling analogues of vitamin D, and intermediates in vitamin D2 and vitamin D3 metabolic pathways against VDR transcriptional activity. The data obtained revealed about significant activation of VDR not only by obligatory ligands calcitriol and ergocalcitriol, but also by their precursors and degradation products.
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Date of publication: 21 June 2016 (Online); Chemical Resistant Toxicology, American Chemical Society
Author Information: Iveta Bartonkova, Aneta Grycova, & Zdenek Dvorak